No area in technology is changing faster than server virtualization. Since the last time we reviewed Microsoft Hyper-V Server 2008 R2 and VMware ESX Server, Microsoft has come out with the next release of its virtualization platform, Hyper-V Server 2008 R2 with SP1, and VMware has released ESX Server 4.1. Both platforms have continued to push the boundaries of virtualization by enhancing their feature sets as well as their performance and scalability.
It should come as no surprise to learn that ESX Server 4.1 remains the enterprise leader in the server virtualization marketplace. However, according to this past year’s Gartner study on virtualization, Hyper-V has seen growth of 127 percent over the past year. Skeptics might say this is because of Microsoft’s much lower market share in the virtualization market, and this is partly true. However, Hyper-V has proven to be a competitive virtualization platform. In this article, I’ll cover some of the most significant changes that have occurred in each platform and then highlight some important characteristics of, and differences between, Hyper-V Server 2008 R2 and ESX Server 4.1.
The Latest Enhancements
With SP1, Microsoft has added some significant new features to Hyper-V Server 2008 R2. The first and most important is Dynamic Memory. Dynamic Memory support lets you better use the available memory on Hyper-V hosts by dynamically allocating host memory to meet the demands of the different virtual machine (VM) workloads that are running. As workloads decrease, memory is returned from the VM to the Hyper-V host.
Another important new feature that Microsoft implemented with SP1 is RemoteFX. RemoteFX is designed to improve the end-user experience for Virtual Desktop Infrastructure (VDI) scenarios, and it enables 3D graphics, the Windows Aero UI, and rich streaming-media experiences in Windows 7 VMs by taking advantage of the graphics-processing power of a DirectX 10-compatible video card on the Hyper-V Server machine. Microsoft also made several significant improvements to Hyper-V in the earlier release of Hyper-V Server 2008 R2, the most important of which was support for Live Migration. Up to that point, Hyper-V only supported Quick Migration. Live Migration is basically the equivalent to VMware VMotion, which allows running VMs to be moved between virtualization hosts with no downtime. Other important new features in the R2 release include support for Second Level Address Translation (SLAT), which provides improved VM performance and scalability and support for up to 64 logical processors on the Hyper-V host. You can find more information about the new features in Hyper-V 2008 R2 SP1 at the Microsoft Hyper-V Server home page.
As for VMware, it has made substantial improvements since its vSphere 4.0 release. Some of the most important new features in the recent vSphere 4.1 release include the ability to boot ESXi from a SAN, improved Call Level Interface (CLI) options for troubleshooting, and seamless user authentication with Active Directory. Some of the main features from the previous vSphere 4.0 release include the ability to hot-add RAM and CPU in a running VM; single-pane management for multiple vCenter servers by using Linked Server mode; the ability to manage multiple VMs as a unit using vApps; fault tolerance, which ensures zero downtime for two single CPU VMs; support for shared memory between VMs; and support for thin virtual disk provisioning. You can find more details about the vSphere 4.1 release at the VMware website.
In future releases, VMware will move away from its ESX Server platform to their thinner vSphere Hypervisor (formerly ESXi). vSphere Hypervisor has a smaller footprint and no service console, which makes it lighter and more secure. You can find out more information about VMware’s move to vSphere Hypervisor at the VMware ESXi and ESX Info Center.
The capabilities offered by Hyper-V and by ESX Server are quite similar. Both offer high degrees of host and VM scalability, and both can provide excellent of server consolidation by supporting up to 1TB of RAM and 64 cores on the virtualization hosts. For VM scalability, Hyper-V Server 2008 R2 supports VMs that have up to 64GB of RAM and four virtual CPUs. ESX Server 4.1 supports VMs that have up to 255GB of RAM and 4 virtual CPUs. The Enterprise Plus edition of vSphere pushes the bar even higher by supporting up to eight virtual CPUs. Table 1 summarizes the primary specifications for Hyper-V Server 2008 R2 and VMware ESX Server 4.1.
Table 1: Hypervisor features
You can see in the table that, although there are differences in the two platforms, they are definitely comparable. Both are excellent for server consolidation, and both provide high degrees of scalability for VMs. In the Windows IT Pro labs, we ran a series of performance tests comparing these two platforms as a small or medium-sized business might use them. In these tests, we used 10 active VMs per host and had 40 clients connected to each VM. The workload was a mix of file serving where some of the clients were reading and writing 135MB files to six of the VMs. The other four VMs were configured as database servers, and the clients were submitting a series of 27 different queries. Under this workload, the performance of the two virtualization platforms was very similar, with the VMware platform eking out a 2 percent overall advantage over Hyper-V. Remember that these tests were designed to assess the performance of each system under an equal load, so they would not be representative of your actual production workloads.
Although Hyper-V Server 2008 R2and vSphere have a lot of similarities, they have just as many differences. Perhaps one of the most important differences between Hyper-V Server 2008 R2 and ESX Server 4.1 concerns the different philosophies behind the way that the two platforms are positioned. VMware views virtualization as an extension of the hardware, whereas Microsoft positions virtualization as a feature of the Windows Server OS. This difference is reflected in the architecture of the two different platforms. You can see a high-level comparison of the architecture of Hyper-V Server 2008 R2 and ESX Server in Figure 1.
Figure 1: Comparing VMware and Hyper-V architectures
Both hypervisors are 64-bit. However, one of the biggest differences between the two products is the way that they handle drivers. ESX Server implements the hardware device drivers as a part of the hypervisor. This makes for a larger hypervisor because the drivers are part of the hypervisor itself. This approach also adds third-party code to the hypervisor. Implementing the device drivers as a part of the hypervisor limits the hardware that ESX Server will run on because it can run only on servers where there are existing drivers. One advantage to this model is that the drivers are specifically tested by VMware for virtualization support.
Microsoft Hyper-V uses the device drivers from the parent partition, outside the hypervisor. Guest VMs run in the child partitions. This allows the Hyper-V hypervisor to be very small, and it contains no third-party code. This approach leverages the Windows driver model, allowing Hyper-V to run on a wide variety of hardware. However, it also places a dependence on the parent partition, and the drivers are not designed specifically to support virtualization.
Guest OS Support
Another big difference between Hyper-V Server 2008 R2 and ESX Server lies in the products’ support of guest OSs. ESX Server is a more mature product, and VMware supports a wide variety of guest OSs. ESX Server 4.1 supports all the Windows Server OSs and most of the popular Linux distributions. Table 2 shows the list of guest OSs that are supported by ESX Server. You can see a complete list of the guest OSs that are supported by ESX Server.
Table 2: ESX Server-supported guest OSs
As you might expect, the list of supported guess OSs for Hyper-V includes all the recent Windows OSs, but few others. Table 3 shows the list of guest OSs that are supported by Hyper-V. This list basically includes all Windows Server OSs, plus SUSE and Red Hat Linux. This Linux implementation is also limited to a single virtual CPU. This falls far short of the Linux support offered by ESX Server. Microsoft has made the code for the Linux Hyper-V Integration components available as open source, but the company has left the adoption of this code to other vendors. You can find more information about the guest OSs supported by Hyper-V Server 2008 R2 at Microsoft's product web page.
Table 3: Hyper-V supported guest OSs
Editions and Licensing
Microsoft delivers Hyper-V in two ways: as a Role in Windows Server 2008 R2 or as the free standalone Hyper-V Server 2008 R2. As part of the Windows Server 2008 OS essentially makes Hyper-V free to organizations that are running Windows Server 2008. Hyper-V is included in the following editions of Windows Server 2008 R2:
- Windows Server 2008 R2 Standard Edition
- Windows Server 2008 R2 Enterprise Edition
- Windows Server R2 Datacenter Edition
Hyper-V Server 2008 R2 supports most of the same features as the Hyper-V role in Windows Server 2008 R2. It supports 32GB or host RAM and VMs that have up to 4 vCPUs. It also supports failover clustering and live migration. You can download Hyper-V 2008 R2 Server at the Microsoft Download Center. You can get more information about the specific differences of Hyper-v Server 20008 R2 and the Hyper-V role Windows Server 2008 R2 at Microsoft's web page.
Like Hyper-V, ESX Server is delivered in two different offerings. First, ESX Server 4.1 is provided as a part of all the different vSphere editions, including vSphere Standard, vSphere Advanced, vSphere Enterprise, and vSphere Enterprise Plus. VMware vSphere is licensed per processor, and the different editions include different feature sets. vSphere Standard is the most basic edition. Building on that, the Advanced edition adds the ability to hot-add CPUs and adds fault tolerance. The Enterprise edition adds Storage VMotion, Distributed Resource Scheduling and the Distributed Power Management. The Enterprise Plus Edition adds eight-way vCPUs and Distributed Switch capabilities. VMware’s added licensing costs make it a more expensive option than Hyper-V. However, it also provides a richer feature set. You can see a complete summary of the different features in each edition at the VMware online store.
VMware also provides a free version of its hypervisor. The free version was formerly known as ESXi, but it has been renamed as vSphere Hypervisor. vSphere Hypervisor is full-featured, and its support for the advanced features in the upper editions of the vSphere suite can be unlocked with a licensing key.
One of the most important considerations in virtualization is licensing, and Microsoft provides some benefits for running Windows Server in a virtual environment. Windows Server 2008 R2 Standard Edition allows for one additional virtual Windows Server instance to run with no additional licensing. The Windows Server 2008 R2 Enterprise Edition license allows up to four additional virtual Windows Server instances to be active. The Windows Server 2008 R2 Datacenter license allows for an unlimited number of virtual Windows Server instances. This licensing applies to any type of virtualization platform, including ESX Server. For example, on the VMware platform, you can license an instance of Windows Server 2008 R2 Datacenter running as a VM on ESX Server, and that license covers all the other active instances of Windows Server on that ESX server.
On the management side, VMware vSphere Client continues to stand head and shoulders above the much more basic Hyper-V Manager from Microsoft. Hyper-V Manager lets you manage the VM on one or more Hyper-V servers. You can create VMs and control them, you can create Virtual LANs (VLANs) by using the new virtual switching feature, you can automatically set up VM start and stop attributes, and you can set VM resource allocations. The Hyper-V Manager is functional, but it does not provide any of the advanced features, such as performance monitoring, that vSphere Client provides.
Although the Hyper-V Manager is the built-in management program for Hyper-V, it’s definitely not Microsoft’s premier virtualization management product—that is System Center Virtual Machine Manager (SCVMM) 2008 R2. SCVMM 2008 R2 is part of System Center Enterprise Suite. Note that System Center Enterprise Suite is not free. There is an Enterprise edition that is licensed for $569 and a Datacenter edition that’s licensed for $2,620.
System Center Enterprise Suite is designed to manage both your physical and virtual infrastructure as a single entity. System Center Operations Manager provides end-to-end monitoring for servers and applications, including VMs. System Center Data Protection Manager enables you to back up your servers and applications. SCVMM 2008 R2 provides a full range of virtualization management tools including templates, self-service provisioning, and administrative delegation. And, when SCVMM 2008 R2 is used in conjunction with System Center Operations Manager, it can form the basis for dynamic systems management. Microsoft is planning a huge update to SCVMM in the second half of 2011. You can see SCVMM 2008 R2 in Figure 2.
Figure 2: Microsoft Virtual Machine Manager
VMWare’s vSphere Client offers a full-featured and functional interface that lets you manage multiple VMware virtual machines for a single ESX Server host. It goes far beyond the capabilities provided by Hyper-V Manager. You can create and control VMs and control several host settings such as the configuration of virtual switches, the host time synchronization, the DNS server, and VM automatic start and stop actions. Additionally, you can use the vSphere Client to set up users and groups along with their associated permissions. One of the best features of the vSphere Client is its ability to track performance information at both the host and VM levels. It provides a storage summary as well as information about CPU, memory, network, and disk usage. Centralized management is provided through VMware vCenter Server. The capabilities provided by the vSphere Client vary according to whether the vCenter Server is installed. You can see the vSphere Client interface in Figure 3.
Figure 3: VMware’s vSphere Client
Pros and Cons
There’s no doubt that Hyper-V is evolving quickly and that it is a perfectly adequate solution for most small and medium businesses. That said, there’s also no doubt that the maturity of vSphere continues to make it the market leader, based on its market share and on the advanced features that are supported by the product. You can see a summary of the pros and cons of Hyper-V Server 2008 R2 and ESX Server in Table 4.
Table 4: Hyper-V and ESX Server summary
A Foundation for the Cloud
Virtualization has proven to be a critical platform for increasing return on investment through server consolidation and by improving availability through technologies such as Live Migration and VMotion. Although many companies are still in the process of implementing virtualization for these reasons, companies such as Microsoft and VMware are working to position virtualization as the basis for the cloud—that is, both the private cloud and the public cloud.